Many devices in use today are capable of outputting audio. These include cell phones, tablets, laptop computers and other mobile devices, desktop computers and others. Such devices typically include an industry-standard analog port that accepts a 3.5 millimeter (mm) plug, sometimes called the “jack plug.” (A less common alternative is a port that accepts a 2.5 mm plug.) The analog port is part of an audio subsystem for outputting audio from the audio device (and in some cases inputting audio into the device), and typically contains two output channels so as to be capable of providing stereo audio output.
A typical headphone to be used with an audio device is an analog output device that includes a plug that fits into the analog port and one or more earpieces. The term “headphone” includes both over-ear devices that are often referred to as “headphones,” as well as in-ear devices that are often called “ear buds,” which often have one earpiece for each channel of a stereo audio output.
Output audio is sent from the audio device by the audio subsystem to the earpiece(s) in the headphone so that a user may listen to the audio output. If the headphone includes two earpieces and the source material has been recorded in a stereo format, one channel will go to each earpiece and the user will hear stereo audio output. Other devices, such as some speakers and amplifiers, may also have a plug that fits into the analog port to receive the output audio.
The use of the analog port is often considered to be advantageous inasmuch as it is simple, easy to use and has become a universal standard. It is also free from license fees, unlike, for example, the digital port on an iPhone® from Apple.
In some cases, is it desirable to provide input to the audio device. The analog subsystem of an audio device typically also has an input channel as part of the analog audio port, but one which only allows for analog audio input. For example, some headphones include a microphone as well as the earpieces so that the user may take part in a telephone call without holding the cell phone up to his ear to hear, or to his mouth to talk. However, such microphones only accept audio input, i.e., the user's voice or other sounds in the vicinity of the microphone, which is received by the audio device on the input channel of the analog audio port.
In addition, in some situations the audio subsystem outputting audio may also simultaneously receive as input external audio received by the headphone itself, if the system is a “hybrid” system. The “hybrid system” has been a well-known feature of the public telephone system for many years. In such a system, the same two wires may carry analog signals in both directions; see, e.g., U.S. Pat. No. 3,180,937.
The transducers in the earpieces of a headphone are activated by signals from the audio device. However, the transducers also respond to air pressure created by sound waves in the area of the earpieces, and create an analog electrical signal in response to that pressure, just as a microphone does. Thus, in the case of an audio device, the wires from the device to the headphone may carry both analog output to the headphone and analog input back from the headphone.
However, even if a headphone is part of a hybrid system and the earpiece of the headphone is able to detect sound waves reaching the earpiece from sources other than the audio device, only audio input will be transmitted back to the device. There appear to be no known instances of a hybrid system carrying any input other than audio.
Some new applications for use on some audio devices also input data to the cell phone through the analog port. One example is the Square Reader from Square, Inc., of San Francisco, Calif., which allows credit cards to be “swiped,” and the cardholder charged, by passing the data from the chip or magnetic stripe on a credit card through an application on a cell phone, tablet or other audio device. However, the Square Reader is actually just another example of the known art, as it also converts the credit card data to audio for inputting to the audio device, and thus the data received by the device is still audio input, just as the audio received from a microphone or headphone in the prior art.
Some applications may benefit from additional data acquisition channels, and from inputting data in a format other than analog audio, for example, in a digital format. In some contemplated applications, for example, health-related applications running on an audio device, various types of biometric data may advantageously be delivered to the audio device to be used by the application. As with the Square Reader, some existing applications attempt to accomplish the input of such biometric data by receiving audio as input on the input channel of the audio subsystem.
In order to allow for the inputting of data in a format other than audio, and particularly digital data, it would be advantageous to be able to use the audio subsystem of an audio device as a data acquisition device by allowing digital data to be input on the audio output channel(s), while not interfering with normal operation of the audio subsystem.